1. Field of the Invention:
This invention relates to a novel self-bonding magnet wire.
2. Description of the Prior Art:
Heretofore, yoke coils used in television sets have been produced by winding wire into a coil shape, subjecting the coil to rapid heating to activate a bonding layer on the wire and pressing the coil into its final shape while the bonding layer is still hot. In such a process, a self-bonding magnet wire having a heat-activated layer on the top of an insulating layer is employed. Heretofore, polyvinyl butyral, alcohol-soluble nylons or the like have been employed as self-bonding layers for self-bonding magnet wires.
In view of the requirements of broadened deflection angles, however, it has recently been desired to minimize the heat distortion of coils and the deformation of coils due to moisture absorption and to maintain adhesion even at high temperatures of about 130.degree.C. With known self-bonding magnet wires using polyvinyl butyrals, alcohol-soluble nylons or the like as a bonding layer, the polyvinyl butyrals show poor resistance to thermal deformation and the nylons inhibit a magnet wire from being smoothly supplied in an automatic winding machine as they give the wires a tacky surface which tends to stick to the bobbin in the winding machine or become tacky due to moisture absorption during storage.
To eliminate the above disadvantages, it has been proposed to add thermosetting resins such as polyester resins, epoxy resins, phenol resins or the like, or these thermosetting resins in combination with hardening agents such as blocked isocyanates or the like, to alcohol-soluble nylons.
For example, the manufacture of a coil-forming insulated electric wire coated with an alcohol-soluble insulating material comprising an alcohol-soluble copolyamide resin and a thermosetting synthetic resin is disclosed, e.g., in U.S. Pat. No. 3,553,011. The conventional coating layer obtained according to this patent however, includes a portion of thermosetting resin which remains unchanged, which is alcohol-soluble, and thus it has poor toughness and resistance against chemicals and is not suited for yoke coils used in television sets, since the step of immersing in alcohols is required at the time of forming a coil.
Furthermore, such reactive varnishes either lose their fusibility if heating is conducted to avoid tackiness of the wires to bobbins, or require high fusion temperatures. As a result, it is difficult to provide products of uniform quality. Further even a self-bonding magnet wire in which tackiness to bobbins is prevented under ordinary conditions as above still becomes tacky under conditions of high temperature and high humidity. Therefore, after the wire is shaped into a coil, deformation thereof by heating or moisture absorption is significant. Accordingly, the requirement of high reliability of deflecting coils has not yet been satisfied.
In order to prevent tackiness of wires to bobbins, it has also been proposed to add acrylonitrile-styrene copolymer resins or polyhydroxy-polyether resins to alcohol-soluble nylons. However, adhesion decreases as compared to the use of nylon alone, and such cannot be considered an acceptable solution to the deformation problems due to heating and moisture absorption.
In order to overcome the above problems, we intensively investigated polyamide resins for forming a bonding layer for a self-bonding magnet wire suitable for use in deflecting coils for television sets.
When we used homopolyamides such as nylon-6, nylon-6,6, etc., the bonding temperature had to be kept too high because homopolyamides of a high melting point are needed. Bonding effected at such a high temperature, however, not only accelerated thermal degradation of the polyamide resins but also of the insulating underlayer if a material of poor heat stability was used therefore. Even nylon-12 which has the lowest melting point among the homopolyamide resins available on an industrial scale requires an undesirably high bonding temperature. Further, if these homopolyamide resins were blended, the desired bonding at low temperatures could not be realized.
However, we found that with a nylon copolymer containing nylon-12, bonding could be obtained at lower temperatures than with nylon-12, and strong adhesion can be obtained even at high temperatures, e.g., 130.degree.C.
Of the nylon copolymers containing nylon-12, however, alcohol-soluble nylons were tacky and apt to cause adhesion of the wire to bobbins, and showed serious heat distortion after the wires were shaped into coils. Hence, they were not suitable as resins for a self-bonding layer. Accordingly, nylon copolymers containing nylon-12 which are capable of providing a self-bonding magnet wire free of tackiness to bobbins and exhibiting good bond strength at high temperatures must be alcohol-insoluble. However, such nylon copolymers were still insufficient in bonding at low temperatures.
In order to obtain bonding at low temperatures using nylon copolymers containing nylon-12, we contemplated blending thermoplastic resins other than nylons, which are capable of bonding at lower temperatures than the nylon copolymers, e.g., polyvinyl butyrals, polyesters, polyether esters, etc. However, if the thermoplastic resins were added in an amount sufficient to lower the bonding temperature, not only was the bond strength at high temperature lost but also resin compatibility was sometimes lost to deteriorate the physical properties of the nylon copolymers per se. Self-bonding magnet wires having such nylon copolymers as a self-bonding layer lost the excellent abrasion resistance and resistance to deterioration in processing which the nylon resins possess.